A conventional portable power amplifier used in portable apparatuses is a simple one because the apparatuses are portable, which regulates a specification of their power amplifiers, so that the power amplifier is not a large size, or does not dissipate heat efficiently. To be specific, as shown in FIG. 7, power amplifying device 2 is mounted on an upper face of printed board 1 disposed in a portable outer case typically used in a portable phone. Heat generated from amplifying device 2 travels through through-holes 3 and is dissipated from pattern 4 prepared on a rear face of printed board 1. However, in this conventional structure, pattern 4 is limited in size as a heat-sink and cannot dissipate heat sufficiently. A use of a dedicated large heat-sink would enlarge the apparatus and make it unfit for portable use.